This invention relates to the conversion and/or hydrotreatment of petroleum or coal derived liquids in an ebullated-bed reactor. The novel processing scheme results in a much simpler and less costly (initial investment and annual operating) ebullated-bed reaction system through the elimination of the high pressure, high temperature separator, hydrogen purification plant, and recycle gas compressor as well as a smaller hydrogen make-up compressor.
This efficiency is accomplished by insuring that the total liquid feed to the reactor (fresh oil feed, ebullating pump recycle and any downstream recycle liquid) is saturated with hydrogen prior to being fed to the reactor and that the quantity of hydrogen dissolved in the liquid is in excess of the quantity chemically consumed via reactions in the ebullated-bed reactor.
In general, ebullated-bed reactors are utilized to process heavy crude oil feed streams, particularly those feeds with high metals and CCR. The ebullated-bed process comprises the passing of concurrently flowing streams of liquids, or slurries of liquids and solids, and gas through a vertically elongated fluidized catalyst bed. The catalyst is fluidized and completely mixed by the upwardly flowing liquid streams. The ebullated-bed process has commercial application in the conversion and upgrading of heavy liquid hydrocarbons and converting coal to synthetic oils.
The ebullated-bed reactor and related process is generally described in U.S. Pat. No. 25,770 to Johanson incorporated herein by reference. A mixture of hydrocarbon liquid and hydrogen is passed upwardly through a bed of catalyst particles at a rate such that the particles are forced into random motion as the liquid and gas pass upwardly through the bed. The catalyst bed motion is controlled by a recycle liquid flow so that at steady state, the bulk of the catalyst does not rise above a definable level in the reactor. Vapors, along with the liquid which is being hydrogenated, pass through the upper level of catalyst particles into a substantially catalyst free zone and are removed from the upper portion of the reactor. The catalyst is used for reacting hydrogen with a petroleum fraction, distillates or resids, for the purpose of saturating or removing sulfur, nitrogen, oxygen, metals or other contaminants, or for molecular weight reduction (cracking). Catalysts having special surface properties are required in order to provide the necessary activity to accomplish the desired reaction(s).
Ebullated-bed reactors are generally operated at relatively high temperatures and pressures in order to process these heavy feedstocks. Since such operating parameters substantially increase the cost of designing and constructing the reactors, it would therefore be advantageous to have a system wherein the overall design and manufacturing costs were optimized for specific feedstocks.
Present commercial ebullated-bed reactors operate with a nominal 1/32 inch extrudate catalyst and at significant superficial gas velocities. The fluidization characteristic of such a system requires an ebullating recycle rate of 2-4 times the feedrate of the heavy oil in order to expand the reactor catalyst bed in the range of 30-50 percent of its settled bed level.
Additionally, the rate of high purity hydrogen containing gas feed to the ebullated-bed reactor is typically in the range of 3-5 times the stoichiometric hydrogen consumed by the feedstock. This relatively high gas feedrate is considered necessary to provide a product vapor phase hydrogen partial pressure of 1,000-2,000 psi (depending on feedstock and reactor severity). The high vapor hydrogen partial pressure insures that the vapor can provide the transfer of sufficient hydrogen to the liquid phase catalytic reacting system. The high rate of gas and the reactor vapor effluent containing significant unreacted hydrogen requires complex and expensive gas treating (separation, hydrogen recovery, recompression, etc.) equipment which can be a large fraction of the investment cost of an ebullated-bed reactor system.
Hence there is a need for an improved and simplified hydroprocessing method and apparatus.